Pulse current generation circuit for neural stimulation, charge compensation circuit and method, and implantable electrical retina stimulator

ABSTRACT

A pulse current generation circuit (100) for neural stimulation includes an analogue signal receiving device (101) for receiving an analogue signal; an analogue-to-digital converter (102) for converting the analogue signal into a digital control signal; a current signal controller (103) for producing, according to the digital control signal, pulse current parameters for generating bidirectional pulse current signals; and a current generator (104) for generating, according to the pulse current parameters, bidirectional pulse current signals for neural stimulation, and the current generator can generate pulse currents of different precisions according to the pulse current parameters. In addition, the present invention further relates to a charge compensation circuit, a charge compensation method, and an implantable electrical retina stimulator using the pulse current generation circuit or the charge compensation circuit.

The present invention relates to a pulse current generation circuit, acharge compensation circuit, a charge compensation method, and animplantable electrical retina stimulator for neural stimulation.

BACKGROUND OF INVENTION

In the field of neural stimulation, nerve tissues respond to electricalstimulations from stimulation electrodes, thereby providing desiredfunctions. For example, in the conventional vision repair system ofartificial retina, in order to restore visual perception to the blind,it is generally necessary to put an implant into an eyeball of theblind. This implant functions as the photoreceptor cells that wereimpaired due to, for example, retinal pigmentation (RP) or age-relatedmacular degeneration (AMD). If other functions of the visual pathway areretained, the stimulation electrodes in the implant can be used tostimulate neural pathways to restore partial vision for the blind.

In an artificial retina system, an external camera outside the bodycaptures video images, and then an image processing device converts thevideo images into electrical signals and sends the electrical signals tothe implant. Then, the implant in the eye converts the electricalsignals into stimulation signals and stimulates ganglion cells in theretina through the stimulation electrodes of the implant, therebyenabling the blind to feel a sense of light in the cerebral cortex andrestore partial vision.

SUMMARY OF INVENTION

However, in conventional artificial retinas or artificial retinalsystems such as implantable electrical retinal stimulators, thestimulation signals generated by the stimulation electrode generally arecapable of stimulating only nerve cells (such as ganglion cells) on thesurface of the retina, and cannot effectively stimulate retinal bipolarcells slightly away from the retina surface. Therefore, the stimulationeffect is seldom good. In addition, there is still much to be improvedin terms of the stimulating resolution.

In addition, in the existing neural stimulation devices such asartificial retina systems, the stimulating current generated for neuralstimulation may not guarantee that the charge amount during onestimulation period falls within a safe range. The nerve tissues (such asretinal ganglion cells or bipolar cells) being stimulated may thereforecarry net charges, such as positive charges or negative charges,resulting in damage to the nerve tissues such as ganglion cells orbipolar cells in the retina.

To balance the stimulating charges received by the nerve tissues such asganglion cells or bipolar cells in the retina, sometimes a RC circuit isarranged between the pulse current generation circuit and a site to bestimulated to balance redundant charges on the ganglion cells or thebipolar cells. However, charge balance performance of the RC circuit ispositively correlated with the capacitance of a capacitor in the RCcircuit. In order to balance more positive or negative charges, thecapacitance of the capacitor in the RC circuit needs to be increased.Thus, a capacitor with a larger size is needed. However, in the field ofneural stimulation, the space for the circuit is often limited, and alarge capacitor occupying large area cannot be integrated into thecircuit. Therefore, the RC circuit cannot fully exert its function incharge balance.

Through long-term researches, the present inventors have found that theganglion cells are connected with multiple bipolar cells in the retina,and the bipolar cells are connected with photoreceptor cells one by onein the macular area of the retina (the place where the artificial retinais usually implanted). By stimulating the bipolar cells in the retina,the stimulating resolution can be effectively improved, therebygenerating a more accurate and effective sense of light. For example,when an implantable electrical retina stimulator is arranged on theretina to restore vision of the blind, the implanted stimulationelectrode is often attached to the retina so that the stimulationelectrode mainly contacts with ganglion cells of the retina (especiallywith the axons of ganglion cells). In order to enable the stimulationsignals generated by the stimulation electrode to stimulate the bipolarcells slightly away from the stimulation electrode, the stimulationelectrode is generally required to provide pulse current of, forexample, a wide pulse width. In addition, to provide a safe chargeamount from the stimulation electrode, if the pulse width of the pulsecurrent is wide, the amplitude of the pulse current shall becorrespondingly reduced to ensure that the stimulation charges arewithin the safe range.

In order to solve the problems mentioned above, the purpose of thepresent invention is to provide a pulse current generation circuitcapable of enhancing effective stimulation resolution, a chargecompensation circuit, a charge compensation circuit method, and animplantable electrical retina stimulator for neural stimulation.

Thus, a first aspect of the present invention provides a pulse currentgeneration circuit for neural stimulation, comprising an analogue signalreceiving device for receiving an analogue signal; ananalogue-to-digital converter for converting the analogue signal into adigital control signal; a current signal controller for producing,according to the digital control signal, pulse current parameters forgenerating bidirectional pulse current signals; and a current generatorfor generating, according to the pulse current parameters, bidirectionalpulse current signals for neural stimulation, wherein the currentgenerator can generate pulse currents of different precisions accordingto the pulse current parameters.

In the first aspect of the present invention, the current signalcontroller generates pulse current parameters for generating thebidirectional pulse current signals based on a digital control signal,and the current generator generates bidirectional pulse current signalswith different precisions for neural stimulation according to the pulsecurrent parameters. By using the current generator which can generatepulse currents of different precisions, bidirectional pulse currentsignals with different pulse widths and different precisions may begenerated according to stimulation needs. Thus, not only the requirementof safe charge can be satisfied, but also the nerve cells (such asbipolar cells) that need to be stimulated can be effectively stimulated,thereby producing more effective stimulation effect. In another aspect,due to the pulse current generation circuit can achieve a wider pulsesignal, therefore, the higher processing requirements can be adapted ata hardware level, such as stimulation algorithm optimization.

In addition, in the pulse current generation circuit according to thepresent invention, optionally, in one stimulation period, the totalcharge amount of the bidirectional pulse current signals is within thesafe charge amount range. Thus, the damage of the pulse current signalto human nerve tissue (such as ganglion cells or bipolar cells inretina) can be avoided, thereby ensuring the safety and the reliabilityof the pulse current generation circuit.

In the pulse current generation circuit according to the presentinvention, optionally, the pulse current parameters include a negativepulse width, a negative pulse amplitude, a positive pulse width, apositive pulse amplitude and a pulse interval. Thus, by controlling thepulse current parameters, different stimulation pulse currents can berealized.

In addition, in the pulse current generation circuit according to thepresent invention, optionally, the current generator generateslow-precision pulse current or high-precision pulse current according tothe pulse current parameters; and the current generator determineswhether bidirectional pulse current signals to be generated are lessthan the critical value after receiving the pulse current parameters,generates the high-precision pulse current when the bidirectional pulsecurrent signals to be generated are less than or equal to the criticalvalue, and generates the low-precision pulse current when thebidirectional pulse current signals to be generated are greater than thecritical value. Thus, the current generator can generate thecorresponding pulse currents in different situations to meet therequirement of the stimulation signal.

In addition, in the pulse current generation circuit according to thepresent invention, optionally, the current generator generates thehigh-precision pulse current when the negative pulse width of thebidirectional pulse current signals is greater than the preset durationand the negative pulse amplitude is less than or equal to the criticalvalue. In this case, nerve cells can be stimulated more effectively.

In addition, in the pulse current generation circuit according to thepresent invention, optionally, the precision of the pulse amplitude ofthe high-precision pulse current is greater than the precision of thepulse amplitude of the low-precision pulse current. Thus, the currentgenerator can generate the pulse currents of different precisionsaccording to actual situations, so as to meet the requirements ofdifferent neural stimulation signals.

In addition, in the pulse current generation circuit according to thepresent invention, optionally, the total charge amount of the positivepulse current or the negative pulse current during one stimulationperiod of the bidirectional pulse current signals is within the safecharge amount range. Thus, long-term safety and reliability of thestimulation electrodes can be ensured.

In addition, a second aspect of the present invention provides a chargecompensation circuit configured for conducting charge compensation onthe pulse current generation circuit which is configured for generatingbidirectional pulse current for neural stimulation; the chargecompensation circuit includes: a detection circuit for detecting thetotal charge amount during one stimulation period of the bidirectionalpulse current signals generated by the pulse current generation circuit;a determination circuit for determining whether the total charge amountdetected by the detection circuit exceeds the safe charge amount range;and a compensation circuit for generating a compensation pulse currentsignal with a net charge amount when the determination circuitdetermines that the total charge amount exceeds the safe charge amountrange, so that the total charge amount is within the safe charge amountrange.

In the second aspect of the present invention, the detection circuit isconfigured for detecting the total charge amount during one stimulationperiod of the bidirectional pulse current signals generated by the pulsecurrent generation circuit, and the determination circuit is configuredfor determining whether the total charge amount detected by thedetection circuit exceeds the safe charge amount range. Moreover, thecompensation circuit is configured for generating a compensation pulsecurrent signal with a net charge amount when the determination circuitdetermines that the total charge amount exceeds the safe charge amountrange, so that the total charge amount is within the safe charge amountrange. In this way, the compensation pulse current signal with a netcharge amount is transmitted to conduct charge balance on thebidirectional pulse current signals under the condition that a largecapacitor (RC circuit) with large occupied area is not used. Thus,charge balance capability can be fully enhanced within a limited space.

In addition, in the charge compensation circuit according to the presentinvention, in the compensation circuit, when the determination circuitdetermines that the total charge amount is a positive value, acompensation pulse current signal with a negative compensation chargeamount is generated so that the total charge amount is within the safecharge amount range; and when the determination circuit determines thatthe total charge amount is a negative value, a compensation pulsecurrent signal with a positive compensation charge amount is generatedso that the total charge amount is within the safe charge amount range.Thus, the total charge amount for neural stimulation is effectivelyensured to be within the safe charge amount range.

In addition, in the charge compensation circuit according to the presentinvention, optionally, the amplitude of the compensation pulse currentsignal is lower than a preset amplitude, and the period of thecompensation pulse current signal is less than the period of thebidirectional pulse current signals. In this case, charge compensationmay be rapidly completed through multiple compensations.

In addition, in the charge compensation circuit according to the presentinvention, optionally, in the bidirectional pulse current signals, awaveform of a positive pulse current signal is opposite to a waveform ofa negative pulse current signal; the detection circuit detects thecharge amount of the positive pulse current signal and an absolute valueof the charge amount of the negative pulse current signal; and thedetermination circuit compares the charge amount of the positive pulsecurrent signal with the absolute value of the charge amount of thenegative pulse current signal to determine whether the total chargeamount exceeds the safe charge amount range.

In addition, in the charge compensation circuit according to the presentinvention, optionally, the detection circuit detects an average value ofthe bidirectional pulse current signals generated by the pulse currentgeneration circuit; the determination circuit determines whether anabsolute value of the average value is greater than a preset value; andwhen the absolute value of the average value is greater than the presetvalue, the compensation circuit generates a compensation pulse currentsignal with a net charge amount, so that the total charge amount iswithin the safe charge amount range. In this case, it can be determinedconveniently whether to provide charge compensation by detecting whetherthe average value is greater than the preset value.

In addition, in the charge compensation circuit according to the presentinvention, optionally, the detection circuit detects a current averagevalue of the bidirectional pulse current signals generated by the pulsecurrent generation circuit, and converts the current average value intoa voltage average value; the determination circuit determines whether anabsolute value of the voltage average value is greater than a presetvoltage value; and when the absolute value of the voltage average valueis greater than the preset voltage value, the compensation circuitgenerates a compensation pulse current signal with a net charge amount,so that the total charge amount is within the safe charge amount range.In this case, the current average value may be converted into thevoltage average value for detection; the absolute value of the voltageaverage value is compared with the preset voltage value; and when theabsolute value of the voltage average value is greater than the presetvoltage value, the total charge amount for neural stimulation is withinthe safe charge amount range through the compensation of thecompensation circuit.

In addition, in the charge compensation circuit according to the presentinvention, optionally, when the absolute value of the voltage averagevalue is greater than the preset voltage value and the voltage averagevalue is a positive value, the compensation circuit generates acompensation pulse current signal with a negative net charge amount sothat the total charge amount for neural stimulation is within the safecharge amount range; and when the absolute value of the voltage averagevalue is greater than the preset voltage value and the voltage averagevalue is a negative value, the compensation circuit generates acompensation pulse current signal with a positive net charge amount sothat the total charge amount for neural stimulation is within the safecharge amount range.

In addition, in the charge compensation circuit according to the presentinvention, the preset amplitude is a minimum current amplitude which canplay a stimulation effect on nerve tissue. Thus, the compensation pulsecurrent signal can be prevented to producing a false stimulation on thenerve tissue.

In addition, a third aspect of the present invention provides a chargecompensation method configured for conducting charge compensation on thepulse current generation circuit which is configured for generatingbidirectional pulse current for neural stimulation. The chargecompensation method includes: detecting the total charge amount duringone stimulation period of the bidirectional pulse current signalsgenerated by the pulse current generation circuit; determining that thetotal charge amount detected by the detection circuit is less than orequal to the safe charge amount; and generating a compensation pulsecurrent signal with a net charge amount when the determination circuitdetermines that the total charge amount exceeds the safe charge amountrange, so that the total charge amount is within the safe charge amountrange.

In addition, in the charge compensation method according to the presentinvention, optionally, when the total charge amount is determined to bea positive value, a compensation pulse current signal with a negativecompensation charge amount is generated so that the total charge amountis within the safe charge amount range; and when the total charge amountis determined to be a negative value, a compensation pulse currentsignal with a positive compensation charge amount is generated so thatthe total charge amount is within the safe charge amount range. Thus,the total charge amount for neural stimulation is effectively ensured tobe within the safe charge amount range.

In addition, a fourth aspect of the present invention provides animplantable electrical retina stimulator, including: an implanted devicehaving at least one of the pulse current generation circuit or thecharge compensation circuit mentioned above; a video recording deviceconfigured to capture a video image and convert the video image into avisual signal; a video processing device connected with the videorecording device and configured to process the visual signal to generatea modulation signal; and an analogue signal transmitting deviceconfigured to transmit the modulation signal to the implanted device,wherein the implanted device converts the received modulation signalinto the bidirectional pulse current signals used as electricalstimulation signals, so as to transmit the bidirectional pulse currentsignals for ganglion cells or bipolar cells of the retina to generate asense of light.

According to the present invention, a more effective stimulation effectcan be generated. Moreover, a higher processing requirement, such asstimulation algorithm optimization, can be adapted at a hardware level.The charge compensation circuit actively compensates possible redundantnet charge on the nerve tissue (such as ganglion cells or bipolarcells), which can improve the efficiency of charge balance onstimulation charge and ensure safety and reliability of neuralstimulation. In addition, under the condition that a large capacitorwith large occupied area is not used, charge balance capability can befully enhanced within a limited space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural schematic diagram showing an implantableelectrical retina stimulator according to a first embodiment of thepresent invention.

FIG. 2 is a schematic diagram showing the implantation of a stimulationelectrode structure of an implantable electrical retina stimulatoraccording to the first embodiment of the present invention into aneyeball.

FIG. 3 is a partial schematic diagram showing the attachment of astimulation electrode structure (a stimulation end) shown in FIG. 2 toretina in an eyeball.

FIG. 4 is a schematic diagram showing a circuit module of a pulsecurrent generation circuit for neural stimulation according to the firstembodiment of the present invention.

FIG. 5 is a schematic diagram showing bidirectional pulse currentsignals according to the first embodiment of the present invention.

FIG. 6 is a schematic diagram showing a circuit module of a currentgenerator according to the first embodiment of the present invention.

FIG. 7 is a schematic diagram showing precisions of different pulsecurrent amplitudes according to the first embodiment of the presentinvention.

FIGS. 8a to 8d are schematic diagrams showing stimulation waveforms ofdifferent bidirectional pulse currents.

FIG. 9 is a structural schematic diagram showing a pulse currentgeneration circuit according to the second embodiment of the presentinvention.

FIG. 10 is a structural schematic diagram showing a charge compensationcircuit according to the second embodiment of the present invention.

FIG. 11 is a schematic diagram showing a compensation pulse currentaccording to the second embodiment of the present invention.

FIG. 12 is a schematic diagram showing a circuit structure of a chargecompensation circuit according to the second embodiment of the presentinvention.

DETAILED DESCRIPTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. In thefollowing description, the same components are denoted by the samereference numerals, and the description thereof will not be repeated. Inaddition, the drawings are merely schematic views, and the ratio of thedimensions of the components to each other or the shapes of thecomponents may be different from the actual ones.

First Embodiment

FIG. 1 is a structural schematic diagram showing an implantableelectrical retina stimulator according to a first embodiment of thepresent invention. FIG. 2 is a schematic diagram showing theimplantation of a stimulation electrode structure of the implantableelectrical retina stimulator according to the first embodiment of thepresent invention into an eyeball. FIG. 3 is a partial schematic diagramshowing the attachment of the stimulation electrode structure (astimulation end) shown in FIG. 2 to the retina in the eyeball.

In the present embodiment, as shown in FIG. 1, the implantableelectrical retina stimulator (sometimes referred to as an “artificialretina” or “artificial retina system”) 1 may include a part implantedinto human body, i.e., an implanted device 10, and apart outside thebody, i.e., an external device 30. In the implantable electrical retinastimulator according to the present embodiment, the implanted device 10and the external device 30 may be coupled wirelessly. In some examples,the implanted device 10 and the external device 30 may be coupled by areceiving antenna 13 and a transmitting antenna 33 shown in FIG. 1. Inaddition, a coupling manner of the implanted device 10 and the externaldevice 30 is not limited thereto in the present embodiment. For example,the implanted device 10 and the external device 30 may also beimplemented in an infrared receiving manner.

In some examples, the implanted device 10 primarily includes a substrate(not shown) as well as an electronic package body 11, a stimulationelectrode structure 12 and the receiving antenna 13 which are disposedon the substrate. In addition, the substrate in the implanted device 10may be fixed to the eyeball 20 in, for example, a stitching manner.

Furthermore, as shown in FIG. 2, a stimulation end 12 a (a stimulationelectrode array) of the stimulation electrode structure 12 in theimplanted device 10 may enter a vitreous cavity of the eyeball 20 via anincision of the eyeball 20, and is close to the retina so that theretina (especially ganglion cells or bipolar cells of the retina) can bestimulated electrically (for example, a bidirectional pulse current isissued) (see FIG. 3).

In general, for example, for patients with retinitis pigmentosa (RP) orage-related macular degeneration (AMD), photoreceptor cells decay or diedue to the RP or AMD, i.e. normal visual pathways are hindered by thelesions of photoreceptor cell diseases, and light that normally enterseyes cannot be converted into visual electrical signals so that thepatients lose the sense of sight. In the present embodiment, thestimulation end 12 a of the stimulation electrode structure 12 isequivalent to replace the photoreceptor cells; and the stimulation end12 a stimulates the ganglion cells or bipolar cells of the retina (seeFIG. 3) by generating electrical stimulation signals, for example,issuing the bidirectional pulse current signals Since most of the visualpathways except the photoreceptor cells are well preserved in mostpatients with the RP or AMD, the electrical stimulation signals aretransmitted to a cerebral cortex via well-preserved downstream visualpathways (optic nerves) and generate the sense of light after theganglion cells or bipolar cells are stimulated by electrical stimulationsignals generated by the stimulation electrode structure 12 so thatvisions of the patients can be restored partially.

In addition, it should be noted that although the present embodimentfocuses on the description of optic neural stimulation of theimplantable electrical retina stimulator, the present embodiment is notlimited to the field of artificial retina, and instead, the pulsecurrent generation circuit 100 according to the present embodiment mayalso be applied to other neural stimulation fields such as cochlearimplants, deep brain stimulation, cardiac pacemakers, spinal cordstimulators.

External Device

In the present embodiment, as shown in FIG. 1, the external device 30may include a video recording device 31, a video processing device 32and the transmitting antenna 33. In the external device 30, the videorecording device 31 may be configured to capture a video image andconvert the captured video image into a visual signal.

In some examples, the video recording device 31 may be a device having avideo recording function such as a video camera, a digital camera, a CCDcamera or the like. For example, an image of the outside world can becaptured by the video recording device 31. Besides, for the convenienceof use, a smaller video camera may be embedded in glasses. Moreover,lightweight glasses having the video recording function may be worn asthe video recording device 31 to capture the video image. Furthermore,the video recording device 31 may also be implemented through GoogleGlass® or the like. In addition, the image may be acquired by ultrasonicimaging (for example, sonar) or electromagnetic wave imaging (forexample, radar), or other devices capable of generating range and angleinformation in the present embodiment.

As shown in FIG. 1, the video processing device 32 is connected with thevideo recording device 31, and receives the visual signal supplied bythe video recording device 31. After the visual signal captured by thevideo recording device 31 is transmitted to the video processing device32, the video processing device 32 can process the visual signal. Insome examples, the video processing device 32 may include amicroprocessor, an application specific integrated circuit (ASIC), DSP,etc. to conduct image processing (such as sampling, encoding,modulation, filtration) on the visual signal. In addition, the videoprocessing device 32 also has a power supply. The power supply mayprovide an energy signal to the implanted device 10, for example, in awireless transmission manner so that the implanted device 10 implantedin the eyeball 20 is powered.

The analogue signal transmitting device (i.e., the transmitting antenna33) may transmit the energy signal provided by the video processingdevice 32 and the processed visual signal as modulation signals (forexample, RF modulation signals) to the implanted device 10 of theartificial retina.

In another aspect, the implanted device 10 may be configured to receivethe modulation signals transmitted by the video processing device 32via, for example, the transmitting antenna 33, and further process themodulation signals to generate the bidirectional pulse current as astimulation current (stimulation signal) for neural stimulation.

Specifically, the receiving antenna 13 (i.e., a specific embodiment ofthe analogue signal receiving device 101 described later) shown in FIG.1 receives the modulation signals and transmits the modulation signalsto a subsequent electronic package body 11 for processing. Finally, theelectrical stimulation signals are generated by the electronic packagebody 11 (specifically, a processing circuit in the electronic packagebody 11) according to the modulation signals and transmitted to thestimulation end 12 a (for example, the stimulation electrode array) ofthe stimulation electrode structure 12, thereby stimulating, forexample, the ganglion cells or bipolar cells of the retina (see FIG. 3).The ganglion cells or bipolar cells generate an excitation responseafter receiving the pulse current to generate the sense of light Inthese cases, the stimulation current may stimulate the ganglion cells ofthe retina or the bipolar cells of the retina, and may also stimulatethe ganglion cells or bipolar cells of the retina at the same time.

Pulse Current Generation Circuit

FIG. 4 is a schematic diagram showing a circuit module of the pulsecurrent generation circuit for neural stimulation according to the firstembodiment of the present invention. FIG. 5 is a schematic diagramshowing the bidirectional pulse current signals according to the firstembodiment of the present invention.

As shown in FIG. 4, the pulse current generation circuit 100 for neuralstimulation according to the present embodiment may include the analoguesignal receiving device 101, an analogue-to-digital converter 102, acurrent signal controller 103 and a current generator 104.

In the present embodiment, the pulse current generation circuit 100 maybe applied to the implantable electrical retina stimulator shown inFIG. 1. In this case, the pulse current generation circuit 100 may belocated in the implanted device 10 shown in FIG. 1.

In some examples, for example, in the implanted device 10, the pulsecurrent generation circuit 100 can generate the bidirectional pulsecurrent signals for stimulating the ganglion cells or bipolar cells ofthe retina. Furthermore, in some examples, the bidirectional pulsecurrent signals generated by the pulse current generation circuit 100can be issued to, for example, the ganglion cells or bipolar cells ofthe retina by the stimulation end 12 a (see FIG. 2) of the stimulationelectrode structure 12 disposed in the implanted device 10.

Analogue Signal Receiving Device

In the present embodiment, the analogue signal receiving device 101 isconfigured to receive an analogue signal in the form of an antenna. Theanalogue signal receiving device 101 transmits the received analoguesignal to the analogue-to-digital converter 102. As described above, theanalogue signal receiving device 101 may be the receiving antenna 13composed of receiving coils. Herein, the coils of the receiving antenna13 may be formed by winding metal wires such as gold wires. In addition,the number of turns of the coils of the receiving antenna 13 is notparticularly limited and may be set as needed.

Analogue-to-Digital Converter

The analogue-to-digital converter 102 can convert the analogue signalreceived by the analogue signal receiving device 101 into a digitalcontrol signal and transmit the digital control signal to the currentsignal controller 103. In the present embodiment, a circuit structure ofthe analogue-to-digital converter 102 is not particularly limited; andanalogue-to-digital converters with different resolutions such as 4bits, 6 bits, 8 bits, 10 bits, 14 bits, 16 bits, etc. may be used asneeded. In addition, the analogue-to-digital converter 102 may be asuccessive approximation type analogue-to-digital converter, a parallelcomparison type analogue-to-digital converter, or an integral typeanalogue-to-digital converter. In addition, the digital control signalmay be a series of digital signal streams, which indicate pulse currentparameters of the bidirectional pulse current signals to be generatedsubsequently.

Current Signal Controller

The current signal controller 103 may produce the pulse currentparameters for generating the bidirectional pulse current signalsaccording to the digital control signal outputted by theanalogue-to-digital converter 102. Herein, the bidirectional pulsecurrent as the stimulation signal may include a positive pulse currentand a negative pulse current. For the neural stimulation field, thecharge of the positive pulse current of the bidirectional pulse currentand the charge of the negative pulse current generally need to be equalto ensure the safety when nerve tissue is stimulated. The effect of thebidirectional pulse current on the neural stimulation will be describedin more detail later.

In some examples, the bidirectional pulse current may be a bidirectionalpulse current of square waveform. In this case, the pulse currentparameters of the bidirectional pulse current may include a negativepulse width t1, a negative pulse amplitude I1, a positive pulse widtht2, a positive pulse amplitude I2 and a pulse interval t3 (see FIG. 5).Herein, the pulse interval t3 refers to a time interval between anegative pulse and a positive pulse. In addition, the time T is astimulation period T described later.

As described above, the current signal controller 103 may produce thepulse current parameters for generating the bidirectional pulse currentsignals according to the digital control signal. In some examples, thedigital control signal can instruct the current controller 103 togenerate the bidirectional pulse current having a wider negative pulsewidth t1 (for example, t1>t2). In other examples, the digital controlsignal may instruct the current controller 103 to generate thebidirectional pulse current having a smaller negative pulse amplitude I1(for example, I1<I2).

Current Generator

The current generator 104 may generate the bidirectional pulse currentsignals for neural stimulation according to the pulse currentparameters. In the present embodiment, since the pulse currentgeneration circuit 100 for neural stimulation can maintain the highprecision of the pulse current while increasing the width of thestimulation pulse current, a more effective current stimulation effectcan be provided, for example, the bipolar cells of the retina can bestimulated effectively. In another aspect, since a wider pulsemodulation range can be realized, higher processing requirements such asstimulation algorithm optimization can be adapted at a hardware level.

In the present embodiment, the current generator 104 may generate atleast two pulse currents of different precision according to the pulsecurrent parameters. In some examples, the current generator 104 cangenerate two pulse currents of different precision. In other examples,the current generator 104 can generate three, four, five or more thanfive pulse currents of different precision. In addition, the differentprecision multiples between the adjacent different pulse currents may betwice, for example, in the situation that current generator 104generates five pulse currents of different precision including a firstpulse current, a second pulse current, a third pulse current, a fourthpulse current and a fifth pulse current, the precision of the fifthpulse current is twice the precision of the fourth pulse current, theprecision of the fourth pulse current is twice the precision of thethird pulse current, the precision of the third pulse current is twicethe precision of the second pulse current, and the precision of thesecond pulse current is twice the precision of the first pulse current.In addition, the present embodiment is not limited thereto, and otherpulse currents of different precisions may also be adopted.

Impedance Load

As shown in FIG. 4, when the current generator 104 conducts neuralstimulation on the nerve tissue or the like, the impedance load 110 isconnected equivalently. For example, when the pulse current generationcircuit 100 according to the present embodiment is configured for neuralstimulation of the artificial retina, the ganglion cells or bipolarcells of the retina in the human tissue fluid may be simplisticallyequivalent to the impedance load 110.

Hereinafter, the current generator 104 according to the presentembodiment will be described in more detail with reference to FIG. 6 andFIG. 7. FIG. 6 is a schematic diagram showing a circuit module of thecurrent generator according to the first embodiment of the presentinvention. FIG. 7 is a schematic diagram showing the precisions ofdifferent pulse current amplitudes according to the first embodiment ofthe present invention. FIGS. 8a to 8d are schematic diagrams showingstimulation waveform of different bidirectional pulse currents.

As shown in FIG. 6, the current generator 104 may include N currentsources. In some examples, the N current sources may be composed of onereference current source 1041 and (N−1) mirror current sources (currentsource arrays). The current sources, for example, are respectivelycontrolled by a switch S1, a switch S2, . . . , and a switch S(N).Herein, the switch S1, the switch S2, . . . , and the switch S(N)control the amplitude of the total pulse current generated by thecurrent generator 104, i.e., the pulse amplitude (positive or negativepulse amplitude) of the total pulse current is proportional to thenumber of closed switches S(N), wherein the switch S1 controls thereference current source 1041. In this case, the total current amplitudeItotal generated by the current generator 104 is equal to (the number ofclosed switches+1) multiplied by the current amplitude of the referencecurrent source.

When the current generator 104 is composed of the N current sourcesmentioned above, the magnitude of the pulse current may be determined bythe opening and closing of (N+1) current sources, and the precision ofthe pulse current may be determined by the size of the reference currentsource 1041. Specifically, the magnitude of the reference current source1041 is the magnitude of the precision of the pulse current. Forexample, if the reference current source 1041 is 1 μA (microamperes),the precision of the pulse current is 1 μA, and a current value of eachmirror current source in (N−1) mirror current sources, i.e., a currentsource 1042, a current source 1043, . . . , and a current source 104(N)is the same as the current value of the reference current source 1041.After the magnitude of the reference current source 1041 is set, thecurrent value of each mirror current source in the current source 1042,the current source 1043, . . . , and the current source 104(N) is equalto the reference current source 1041.

In some examples, if the number of the reference current sources 1041and the (N−1) mirror current sources is N=512 in total, and theprecision of the reference current source 1041 is set to 1 μA, thecurrent generator 104 may generate a pulse current having the precisionof 1 μA and 512 pulse amplitudes, i.e., the current generator 104 maygenerate a total of 512 different current amplitudes including 1 μA, 2μA, 3 μA, . . . , and 512 μA by controlling the switch S1, the switchS2, . . . , and the switch S(N). In other examples, if the number of thereference current sources 1041 and the (N−1) mirror current sources isN=512 in total, and the precision of the reference current source 1041is set to 4 μA, the current generator 104 may generate a pulse currenthaving the precision of 4 μA and 128 pulse amplitudes, i.e., the currentgenerator 104 may generate a total of 128 different current amplitudesincluding 4 μA, 8 μA, 12 μA, . . . , and 512 μA by controlling theswitch S1, the switch S2, . . . , and the switch S(N). In some otherexamples, if the number of the reference current sources 1041 and the(N−1) mirror current sources is N=512 in total, and the precision of thereference current source 1041 is set to 8 μA, the current generator 104may generate a pulse current having the precision of 8 μA and 64 pulseamplitudes, i.e., the current generator 104 may generate a total of 64different current amplitudes including 8 μA, 16 μA, 24 μA, . . . , and512 μA by controlling the switch S1, the switch S 2, ..., and the switchS(N). Although the current precisions 1 μA, 4 μA and 8 μA are introducedas examples in the above description, the present embodiment is notlimited thereto, and the pulse current generation circuit 100 accordingto the present embodiment may also generate currents having, forexample, 2 μA, 6 μA, 12 μA and other precisions.

As described above, since different current precisions may be realizedby setting the reference current sources 1041 of different currentmagnitudes, the precisions of the generated pulse currents can be set bysetting a plurality of different reference current sources in thepresent embodiment, so that a plurality of pulse currents of differentprecisions can be generated. In the present embodiment, two differentreference current sources may be set, and pulse currents of twodifferent precisions (high precision and low precision) may be realizedin this case.

In some examples, the current generator 104 may generate thebidirectional pulse currents of two different precisions including afirst pulse amplitude precision (high precision) and a second pulseamplitude precision (low precision). For example, a first pulseamplitude precision may be set to 1 μA/step, the range of currentamplitude is 0-8 μA; and a second pulse amplitude precision may be setto 8 μA/step, the range of current amplitude is 8-512 μA (see FIG. 7).Herein, the precision (the first pulse amplitude precision is 1 μA/step)of the pulse amplitude of the high-precision pulse current is greaterthan the precision (the second pulse amplitude precision is 8 μA/step)of the pulse amplitude of the low-precision pulse current. Thus, thecurrent generator 104 may generate the pulse currents of differentprecisions according to actual conditions to meet the requirements ofdifferent neural stimulation signals. In addition, in other examples,the current generator 104 may provide more pulse currents of differentprecisions.

Bidirectional Pulse Current Signals

In some examples, the total charge amount during one stimulation periodT of the bidirectional pulse current signals generated by the currentgenerator 104 is within the safe charge amount range (for example, thetotal charge amount is zero). Specifically, in the neural stimulationfield, in order to prevent the pulse current signal from generating anet charge on human nerve tissue such as ganglion cells or bipolar cellsof the retina to damage the human nerve tissue, it should be ensuredthat the total charge amount of the bidirectional pulse current signalsduring one stimulation period T is within the safe charge amount range.

Herein, the “safe charge amount” is the maximum value of the net chargewhich can be withstood by the nerve tissue (for example, the ganglioncells or bipolar cells of the retina) within a safe range. The netcharge exceeding the safe charge amount range may cause damage to thenerve tissue. Herein, one stimulation period T is a period time at whicha stimulation signal is generated. Therefore, during actual neuralstimulation, it should be ensured that the total charge amount duringone stimulation period T is controlled within the safe charge amountrange. Herein, one stimulation period T is a period time at which astimulation signal is generated. The total charge amount refers to thetotal charge amount of the net charge of the bidirectional pulse currentsignals during one stimulation period T. In some examples, the safecharge amount may also be set to zero for convenience.

In addition, in the present embodiment, if it is ensured that the totalcharge amount of the bidirectional pulse current during one stimulationperiod T is within the safe charge amount range, the waveform of thepulse current is not limited. FIGS. 8a-8d show schematic diagrams ofstimulation waveforms of different bidirectional pulse currents. Sincethe negative pulse current is usually used as an effective stimulationsignal in the neural stimulation field, modified examples of thebidirectional pulse current signals are illustrated by taking thenegative pulse waveform as an example in FIGS. 8a -8 d.

As shown in FIGS. 8a-8d , for the bidirectional pulse current signals asthe stimulation waveforms, the waveform of the negative pulse and thewaveform of the positive pulse are not necessarily the same, but it isensured that the total charge amount of the bidirectional pulse currentsignals during one stimulation period T is within the safe charge amountrange. As an example, the negative pulse widths t11, t12, t13 and t14may each be greater than the positive pulse width t2, thereby realizinga wide stimulation pulse. In addition, the bidirectional pulse currentmay be a bidirectional square wave pulse current signal, or a cosinepulse current signal, or a combination of the square wave pulse currentsignal and the cosine pulse current signal.

As described above, the current generator 104 may generate thebidirectional pulse current signals according to the pulse currentparameters. Specifically, the bidirectional pulse current signals mayinclude effective stimulation current signals and balanced currentsignals, wherein the effective stimulation current signals are currentsignals having a stimulating effect on neural stimulation objects suchas the ganglion cells or bipolar cells; and the balanced current signalsare current signals for balancing the charge generated by the effectivestimulation current signals. Generally, if the effective stimulationsignals are positive pulses, the balanced current signals are negativepulses; if the effective stimulation signals are negative pulses, thebalanced current signals are positive pulses. Thus, it can be ensuredthat the total charge amount of the bidirectional pulse current signalsduring one stimulation period T is within the safe charge amount range.(For example, the total charge amount is zero).

In the present embodiment, as described above, the current signalcontroller 103 produces the pulse current parameters for generating thebidirectional pulse current signals Thus, the total charge amount of thebidirectional pulse current signals theoretically generated by thecurrent generator 104 during one stimulation period is within the safecharge amount range by setting the pulse current parameters. Inaddition, in order to suppress the influence of the net charge which maybe accumulated by the stimulation current signals on a human body, thebidirectional pulse current signals are usually set such that only oneof the positive pulse and the negative pulse is the stimulation signal,and the other is the balanced current signal. Thus, it is ensured thatthe total charge amount of the bidirectional pulse current signalsduring one stimulation period T is within the safe charge amount range.

As a specific example, during one stimulation period T, an integral ofthe negative pulse signal of the bidirectional pulse current signals intime may be equal to an absolute value of the integral of the positivepulse signal of the bidirectional pulse current signals in time. Thus,the total charge amount of the bidirectional pulse current signalsduring one stimulation period T is within the safe charge amount range.In addition, with reference to FIG. 5, as shown in FIG. 5, during onestimulation period T, if the duration of the negative pulse signal (thenegative pulse width) is t1, and the duration of the positive pulsesignal (the positive pulse width) is t2, the absolute value of theintegral of the negative pulse in the duration t1 is equal to theabsolute value of the integral of the positive pulse in the duration t2,i.e., the total charge amount of the bidirectional pulse current signalsis within the safe charge amount range (for example, the total chargeamount is zero).

As described above, the current generator 104 provides two differentpulse amplitude precisions including a first pulse amplitude precisionand a second pulse amplitude precision, wherein the first pulseamplitude precision is 1 μA/step, and the amplitude range is 0-8 μA (forexample, 1 μA, 2 μA, 3 μA, . . . , and 8 μA); the second pulse amplitudeprecision is 8 μA/step, and the amplitude range is 8-512 μA (forexample, 8 μA, 16 μA, 24 μA, . . . , and 512 μA) (see FIG. 7).

In some examples, as shown in FIG. 7, when the neural stimulationobjects such as the ganglion cells or bipolar cells of the retinarequire a lower pulse current stimulation, the current generator 104 mayprovide a higher pulse amplitude precision (for example, 1 μA/step). Forexample, when the current amplitude required by the ganglion cells orbipolar cells is less than or equal to 8 μA, the current has the pulseamplitude precision of 1 μA/step and is capable of providing a total of8 pulse amplitudes including 1 μA, 2 μA, 3 μA, 4 μA, 5 μA, 6 μA, 7 μAand 8 μA; and when the current required by the ganglion cells or bipolarcells is greater than 8 μA, the current has the pulse amplitudeprecision of 8 μA/step and is capable of providing a total of 64 pulseamplitudes including 16 μA, 24 μA, 32 μA, 40 μA, . . . 512 μA.

In the present embodiment, the current generator 104 may provide pulseamplitudes of at least two different precisions and generate pulsecurrents of at least two different precisions, thereby, a more efficientcurrent stimulation manner can be provided.

In some examples, the current generator 104 may generate thelow-precision pulse current or the high-precision pulse currentaccording to the pulse current parameters. Specifically, the currentgenerator 104 determines whether the pulse amplitude of thebidirectional pulse current signals to be generated is less than acritical value after receiving the pulse current parameters. When thepulse amplitude of the bidirectional pulse current signals to begenerated is less than or equal to the critical value, the currentgenerator 104 generates the high-precision pulse current; and when thepulse amplitude of the bidirectional pulse current signals to begenerated is greater than the critical value the current generator 104generates the low-precision pulse current. Thus, the current generator104 may generate corresponding pulse currents under different conditionsto meet the requirements of different neural stimulation signals.

In the present embodiment, the critical value may be set in advance. Inaddition, the amplitude precision of the high-precision pulse currentand the amplitude precision of the low-precision pulse current may alsobe set in advance. For example, as shown in FIG. 7, the critical valuemay be set to 8 μA, the amplitude precision of the high-precision pulsecurrent is 1 μA/step, and the amplitude precision of the low-precisionpulse current is 8 μA/step.

In this case, when the current generator 104 determines that theamplitude of the bidirectional pulse current signals to be generated isless than or equal to 8 μA, the current generator 104 generates thehigh-precision (1 μA/step) pulse current; and when the current generator104 determines that the amplitude of the bidirectional pulse currentsignals to be generated is greater than 8 μA, the current generator 104generates the low-precision (8 μA/step) pulse current. In this way, thecurrent generator 104 may provide the pulse currents of two differentprecisions. When the ganglion cells or bipolar cells require a smallerpulse current, the high-precision pulse current is provided so that thebipolar cells of the retina can be stimulated more accurately, and themore efficient stimulation manner can be provided.

In some examples, when the positive pulse width of the bidirectionalpulse current signals is greater than a preset duration and the positivepulse amplitude is less than the critical value, or when the negativepulse width of the bidirectional pulse current signals is greater thanthe preset duration and the negative pulse amplitude is less than thecritical value, the current generator 104 generates the high-precisionpulse current.

For the width (stimulation time) of the stimulation pulse current,although the action mechanism is still unclear, deeper nerve cells aremore likely stimulated by extending the stimulation pulse width (forexample, the negative pulse width), thereby, more efficient neuralstimulation can be acquired. For example, for the implantable electricalretina stimulator, a wide stimulation pulse can stimulate the bipolarcells of the retina more effectively, thereby, more effective and moreprecise neural stimulation can be provided.

Specifically, when the negative pulse width of the bidirectional pulsecurrent signals is greater than the preset duration and the negativepulse amplitude is less than the critical value, the bidirectional pulsecurrent signals can stimulate the bipolar cells of the retina moreprecisely. Since the one-to-one correspondence of the bipolar cells inthe visual pathways is superior to that of the ganglion cells, theprecise stimulation of the bipolar cells may form a more accurate senseof light. In addition, higher processing requirements such asstimulation algorithm optimization can also be adapted at a hardwarelevel.

In this way, when the positive pulse width of the bidirectional pulsecurrent signals is greater than the preset duration and the positivepulse amplitude is less than the critical value, or when the negativepulse width of the bidirectional pulse current signals is greater thanthe preset duration and the negative pulse amplitude is less than thecritical value, the current generator 104 generates the high-precisionpulse current for precisely stimulating the bipolar cells to form a moreaccurate sense of light, thereby providing a more efficient stimulationmanner for the blind.

Second Embodiment

FIG. 9 is a schematic diagram showing a circuit structure of a pulsecurrent generation circuit according to the second embodiment of thepresent invention. FIG. 10 is a schematic diagram showing a circuitstructure of a charge compensation circuit according to the secondembodiment of the present invention. FIG. 11 is a schematic diagramshowing a compensation pulse current according to the second embodimentof the present invention. FIG. 12 is a schematic diagram showing acircuit structure of the charge compensation circuit according to thesecond embodiment of the present invention.

The pulse current generation circuit 200 according to the secondembodiment differs from the pulse current generation circuit 100according to the first embodiment in that besides the analogue signalreceiving device 101, the analogue-to-digital converter 102, the currentsignal controller 103 and the current generator 104 according to thefirst embodiment, the charge compensation circuit 106 is also included.

Furthermore, it should be noted that although the present embodimentfocuses on the description of the visual stimulation of the implantableelectrical retina stimulator, however, the present embodiment is notlimited to the field of artificial retina, and instead, the chargecompensation circuit 106 according to the present embodiment may also beapplied to other neural stimulation fields such as cochlear implants,deep brain stimulation, cardiac pacemakers, spinal cord stimulators.

As shown in FIG. 9, the charge compensation circuit 106 for neuralstimulation is according to the present embodiment. In the presentembodiment, the charge compensation circuit 106 can be applied to theimplantable electrical retina stimulator shown in FIG. 1. In this case,the charge compensation circuit 106 may be located in the implanteddevice 10 (for example, within the electronic package body 11) shown inFIG. 1. Specifically, the pulse current generation circuit 200 may belocated in the electronic package body 11 shown in FIG. 1. In thepresent embodiment, the charge compensation circuit 106 may beconfigured to conduct charge compensation on the pulse currentgeneration circuit 200.

In the present embodiment, as shown in FIG. 10, the charge compensationcircuit (also referred to as “active charge compensation circuit”) 106includes a detection circuit 10621, a determination circuit 1062 and acompensation circuit 1063. The detection circuit 1061 may be configuredto detect a total charge amount during one stimulation period T of thebidirectional pulse current signals generated by the pulse currentgeneration circuit 200.

In addition, the determination circuit 1062 may be configured todetermine whether the total charge amount detected by the detectioncircuit 1061 exceeds the safe charge amount range. Furthermore, thecompensation circuit 1063 may be configured to generate a compensationpulse current signal with a net charge amount when the determinationcircuit 1062 determines that the total charge amount exceeds the safecharge amount range so that the total charge amount for neuralstimulation is within the safe charge amount range. Herein, the netcharge amount may be a negative charge amount or a positive chargeamount based on the case where compensation is required.

Theoretically, the pulse current parameters (for example, the pulsecurrent parameters may include a positive pulse width, a positive pulseamplitude, a positive pulse amplitude, a negative pulse width, anegative pulse amplitude, a pulse interval, etc.) of the bidirectionalpulse current signals can be set such that the total charge amount ofthe bidirectional pulse current signals during one stimulation period Tis within the safe charge amount range. However, in an actualapplication circuit, the total charge amount of the bidirectional pulsecurrent signals generated by the pulse current generation circuit 200during one stimulation period T is likely to exceed the safe chargeamount range due to various factors. In this case, the net chargeaccumulated by the bidirectional pulse current signals may cause damageto the ganglion cells or bipolar cells of human eyes.

In the present embodiment, redundant net charge accumulated on nervetissue (for example, the ganglion cells or bipolar cells) is activelycompensated by the charge compensation circuit 106 so that the abilityto balance the stimulation charge can be improved and the safety andreliability of neural stimulation can be ensured, thereby playing a roleof protecting human nerve tissue such as the ganglion cells or bipolarcells of the retina.

In the present embodiment, the detection circuit 1061 can be configuredto detect the total charge amount during one stimulation period T of thebidirectional pulse current signals generated by the pulse currentgeneration circuit 200. Next, the determination circuit 1062 determineswhether the total charge amount during one stimulation period T of thebidirectional pulse current signals detected by the detection circuit1061 exceeds the safe charge amount range. If the total charge amountduring one stimulation period T of the bidirectional pulse currentsignals is within the safe charge amount range, the compensation circuit1063 does not work; and if the total charge amount during onestimulation period T of the bidirectional pulse current signals exceedsthe safe charge amount range, the compensation circuit 1063 generates acompensation pulse current signal with a net charge amount, so that thetotal charge amount for neural stimulation is within the safe chargeamount range.

Specifically, when the determination circuit 1062 determines that thetotal charge amount during one stimulation period T of the bidirectionalpulse current signals is a positive charge, the compensation circuit1063 produces a negative current pulse so that the total charge amountfor neural stimulation is within the safe charge amount range. When thedetermination circuit 1062 determines that the total charge amountduring one stimulation period T of the bidirectional pulse currentsignals is a negative charge, the compensation circuit 1063 produces apositive current pulse so that the total charge amount for neuralstimulation is within the safe charge amount range.

In the present embodiment, the compensation circuit 1063 may activelyconduct charge compensation. Once the determination circuit 1062determines that the total charge amount during one stimulation periodproduced by the pulse current generation circuit 200 and detected by thedetection circuit 1061 exceeds the safe charge amount range, thecompensation circuit 1063 may conduct charge compensation in time,thereby enhancing charge balance efficiency or capability and ensuringsafety of the stimulated nerve tissue.

In some examples, the compensation circuit 1063 may generate acompensation pulse current signal with a net charge amount when thedetermination circuit 1062 determines that the total charge amountduring one stimulation period T of the bidirectional pulse currentsignals exceeds the safe charge amount range, so that the total chargeamount for neural stimulation is within the safe charge amount range. Inaddition, the compensation circuit 1063 may generate a compensationpulse current signal with a positive net charge amount when thedetermination circuit 1062 determines that the total charge amountduring one stimulation period T of the bidirectional pulse currentsignals is less than zero, so that the total charge amount for neuralstimulation is within the safe charge amount range.

For example, when the determination circuit 1062 determines that thetotal charge amount during one stimulation period T of the bidirectionalpulse current signals is negative charge of −1×10−7 coulombs, thecompensation circuit 1063 produces positive charge with a total chargeamount of 1×107 coulombs (for example, the compensation circuit 1063 mayproduce a positive pulse with a pulse width of 1 millisecond and a pulseamplitude of 100 microamps, or the compensation circuit 1063 may producea positive pulse with a pulse width of 10 milliseconds and a pulseamplitude of 10 microamps), so that the total charge amount for neuralstimulation is within the safe charge amount range. For example, whenthe determination circuit 1062 determines that the total charge amountduring one stimulation period T of the bidirectional pulse currentsignals is positive charge of 1×10−7 coulombs, the compensation circuit1063 produces negative charge with a total charge amount of −1×10−7coulombs (for example, the compensation circuit 1063 may produce anegative pulse with a pulse width of 1 millisecond and a pulse amplitudeof 100 microamps, or the compensation circuit 1063 may produce anegative pulse with a pulse width of 10 milliseconds and a pulseamplitude of 10 microamps), so that the total charge amount for neuralstimulation is within the safe charge amount range.

In the present embodiment, the amplitude of the compensation pulsecurrent signal may be lower than a preset amplitude, and the period ofthe compensation pulse current signal may be less than the period of thebidirectional pulse current signals. Herein, the preset amplitude is aminimum current amplitude which can play a stimulation effect on nervetissue (such as ganglion cells or bipolar cells). The amplitude of thecompensation pulse current signal is set to be lower than the presetamplitude so as to prevent the compensation pulse current signal fromproducing a false stimulation on the nerve tissue (such as ganglioncells or bipolar cells) and inhibiting the nerve tissue (such asganglion cells or bipolar cells) from producing unnecessary excitementdue to possible reception of the compensation pulse current signal. Inaddition, the period of the compensation pulse current signal may alsobe set to be less than the period of the bidirectional pulse currentsignals. Thus, charge compensation may be conducted within short time.For example, charge compensation may be conducted rapidly throughmultiple compensations.

In some examples, in the bidirectional pulse current signals, a waveformof a positive pulse current signal may be opposite to a waveform of anegative pulse current signal. Namely, in the bidirectional pulsecurrent signals, the waveform of the pulse currents are identical exceptthat the waveform of the positive pulse current signal is opposite tothe waveform of the negative pulse current signal. In this way, thedetection circuit 1061 may detect the charge amount of the positivepulse current signal and an absolute value of the charge amount of thenegative pulse current signal. Then, the determination circuit 1062compares the charge amount of the positive pulse current signal with theabsolute value of the charge amount of the negative pulse current signalto determine whether the total charge amount exceeds the safe chargeamount range.

Again referring to FIG. 5, FIG. 5 is a schematic diagram showingbidirectional pulse current signals according to the embodiment of thepresent invention. As shown in FIG. 5, the bidirectional pulse currentsignals may include a positive pulse signal and a negative pulse signal,and the waveform of the positive pulse current signal is opposite to thewaveform of the negative pulse current signal. At this moment, thedetection circuit 1061 may detect the charge amount of the positivepulse current signal and the absolute value of the charge amount of thenegative pulse current signal. For example, the charge amount of thepositive pulse current signal is Q1=I1×t1, and the absolute value of thecharge amount of the negative pulse current signal is Q2=|I2×t2|, and|I2×t2| is the absolute value of I2×t2. Next, the determination circuit1062 determines a difference between the charge amount Q1 and the chargeamount Q2, i.e., the total net charge amount=Q1-Q2. When the chargeamount Q1 is equal to the charge amount Q2, the total charge amount isdetermined to be zero. When the charge amount Q1 is not equal to thecharge amount Q2, the total charge amount is determined not to be zero,wherein when the charge amount Q1 is greater than the charge amount Q2,the total charge amount is determined to be a positive value (there is apositive net charge); and when the charge amount Q1 is less than thecharge amount Q2, the total charge amount is determined to be a negativevalue (there is a negative net charge). In addition, the above totalcharge amount shall be ensured to be within the safe charge amount rangeregardless of the positive net charge and the negative net charge.

In some examples, the detection circuit 1061 may detect an average valueof the bidirectional pulse current signals generated by the pulsecurrent generation circuit 200. Specifically, the net charge amountsbetween the negative charge amount and the positive charge amount of thebidirectional pulse current signals is directly computed, and the netcharge amounts are averaged, thereby obtaining that whether a net chargeexists in the total charge amount of the bidirectional pulse currentsignals generated by the pulse current generation circuit 200. Then, thedetermination circuit 1062 may determine whether an absolute value ofthe average value is greater than a preset value; and when the absolutevalue of the average value is greater than the preset value, thecompensation circuit 1063 may generate a compensation pulse currentsignal with a net charge amount, so that the total charge amount forneural stimulation is within the safe charge amount range.

In the present embodiment, the average value of the bidirectional pulsecurrent signals may be a current average value, an average charge value,etc. of the bidirectional pulse current signals. In addition, the presetvalue may be a preset current value, a preset charge value, etc.

In some examples, the average value of the bidirectional pulse currentsignals may be the current average value of the bidirectional pulsecurrent signals In this case, the detection circuit 1061 may detect thecurrent average value of the bidirectional pulse current signals,Ia=|(I1×t1+I2×t2)/(t1+t2)|, wherein I2 is a negative value. The presetcurrent value is set as I′ (I′>0), and the determination circuit 1062may determine whether Ia is greater than I′. If Ia is greater than I′,then the compensation circuit 1063 generates a compensation pulsecurrent signal with a net charge amount so that the total charge amountfor neural stimulation is within the safe charge amount range. If Ia isless than or equal to I′, then the compensation circuit 1063 does notwork

In some examples, the average value of the bidirectional pulse currentsignals may be the average charge value of the bidirectional pulsecurrent signals. In this case, the detection circuit 1061 may detect theaverage charge value of the bidirectional pulse current signals,Qa=|(I1×t1+I2×t2)/2|, wherein I2 is a negative value. The preset chargevalue is set as Q′ (Q′>0), and the determination circuit 1062 maydetermine whether Qa is greater than Q′. If Qa is greater than Q′, thenthe compensation circuit 1063 generates a compensation pulse currentsignal with a net charge amount so that the total charge amount forneural stimulation is within the safe charge amount range. If Qa is lessthan or equal to Q′, then the compensation circuit 1063 does not work.

In some examples, the detection circuit 1061 may detect the currentaverage value of the bidirectional pulse current signals generated bythe pulse current generation circuit 200, and converts the currentaverage value into a voltage average value. In this case, thedetermination circuit 1062 may determine whether the absolute value ofthe voltage average value is greater than the preset voltage value. Inthis case, when the absolute value of the voltage average value isgreater than the preset voltage value, the compensation circuit 1063 maygenerate a compensation pulse current signal with a net charge amount sothat the total charge amount for neural stimulation is within the safecharge amount range.

For example, the current average value is converted into the voltageaverage value through a current and voltage conversion circuit, and thepreset voltage value is set as a safe voltage value. When the voltageaverage value is lower than the preset voltage value, it indicates thatthe bidirectional pulse current signals generated by the pulse currentgeneration circuit 200 have no damage to human ganglion cells or bipolarcells (without exceeding the safe charge amount range), and thecompensation circuit 1063 does not need to conduct charge compensation.When the voltage average value is higher than the preset voltage value,it indicates that the bidirectional pulse current signals generated bythe pulse current generation circuit 200 may have damage to humanganglion cells or bipolar cells and the compensation circuit 1063generates a compensation pulse current signal with a net charge amountso that the total charge amount for neural stimulation is within thesafe charge amount range.

In the present embodiment, the detection circuit 1061 converts thedetected average current value into the voltage average value which iseasily determined by the determination circuit 1062 (for example, thedetermination circuit 1062 may determine using a voltage comparator); itis convenient for the determination circuit 1062 to determine whetherthe compensation circuit 1063 needs charge compensation; and theaccuracy of the outcome of the determination circuit 1062 can beenhanced.

In addition, in some examples, when the absolute value of the voltageaverage value is greater than the preset voltage value and the voltageaverage value is a positive value, the compensation circuit 1063 maygenerate a compensation pulse current signal with a negative net chargeamount so that the total charge amount for neural stimulation is withinthe safe charge amount range; and when the absolute value of the voltageaverage value is greater than the preset voltage value and the voltageaverage value is a negative value, the compensation circuit 1063generates a compensation pulse current signal with a positive net chargeamount so that the total charge amount for neural stimulation is withinthe safe charge amount range.

In the present embodiment, the detection circuit 1061 may detect acurrent average value of the bidirectional pulse current signalsgenerated by the pulse current generation circuit 200, and converts thecurrent average value into a voltage average value. The determinationcircuit 1062 may determine whether an absolute value of the voltageaverage value is greater than a preset voltage value. When the absolutevalue of the voltage average value is greater than the preset voltagevalue and the voltage average value is a positive value, thecompensation circuit 1063 generates a compensation pulse current signalwith a negative net charge amount, so that the total charge amount iswithin the safe charge amount range. When the absolute value of thevoltage average value is greater than the preset voltage value and thevoltage average value is a negative value, the compensation circuit 1063generates a compensation pulse current signal with a positive net chargeamount, so that the total charge amount for neural stimulation is withinthe safe charge amount range.

For example, if the preset voltage value is 5 millivolt (mv), when thevoltage average value is greater than 5 mv (i.e., the absolute value ofthe voltage average value is greater than the preset voltage value andthe voltage average value is a positive value), the compensation circuit1063 generates a compensation pulse current signal with a negative netcharge amount, so that the total charge amount for neural stimulation iswithin the safe charge amount range. For example, the compensation pulsecurrent signal generated by the compensation circuit 1063 is a negativepulse. In addition, when the voltage average value is less than −5 mv(i.e., the absolute value of the voltage average value is greater thanthe preset voltage value and the voltage average value is a negativevalue), the compensation circuit 1063 generates a compensation pulsecurrent signal with a positive net charge amount, so that the totalcharge amount for neural stimulation is within the safe charge amountrange. For example, the compensation pulse current signal generated bythe compensation circuit 1063 is a positive pulse.

FIG. 11 is a schematic diagram showing a circuit structure of a chargecompensation circuit according to the embodiment of the presentinvention. As shown in FIG. 11, the charge compensation circuit 106 mayinclude a detection circuit 1061, a determination circuit 1062 and acompensation circuit 1063. In the present embodiment, the detectioncircuit 1061 may specifically include a first resistor R1, a secondresistor R2 and a capacitor C1, wherein a negative pole of the firstcapacitor and a first end of the first resistor R1 are connected to acommon voltage VSS; a positive pole of the first capacitor and a secondend of the first resistor R1 are electrically connected to a second endof the second resistor R2; and a first end of the second resistor R2 iselectrically connected to the pulse current generation circuit 200 andthe compensation circuit 1063.

In addition, the determination circuit 1062 may specifically include afirst voltage comparator U1 and a second voltage comparator U2, whereinan in-phase input end of the first voltage comparator U1 and an in-phaseinput end of the second voltage comparator U2 are electrically connectedto the first end of the second resistor R2; a reverse-phase input end ofthe first voltage comparator U1 is connected to a preset positivevoltage VTH+; a reverse-phase input end of the second voltage comparatorU2 is connected to a preset negative voltage VTH−; a power supply end ofthe first voltage comparator U1 and a power supply end of the secondcomparator U2 are connected to a power voltage VDD; a grounding end ofthe first voltage comparator U1 and a grounding end of the secondcomparator U2 are connected to the common voltage VSS; an output endOut1 of the first voltage comparator U1 is electrically connected to afirst control end C+ of the compensation circuit 1063; an output endOut2 of the second voltage comparator U2 is electrically connected to asecond control end C− of the compensation circuit 1063; a power supplyend of the compensation circuit 1063 is connected to the power voltageVDD; a grounding end of the compensation circuit 1063 is connected tothe common voltage VSS; an output end of the compensation circuit 1063is connected to the input end of the pulse current generation circuit200; a power supply end of the pulse current generation circuit 200 isconnected to the power voltage VDD; a grounding end of the pulse currentgeneration circuit 200 is connected to the common voltage VSS; and anoutput end of the pulse current generation circuit 200 is connected tothe impedance load 110.

In addition, the detection circuit 1061 may detect a total charge amountin one stimulation period T and a current average value in onestimulation period T for the bidirectional pulse current signalsgenerated by the pulse current generation circuit 200, and converts thecurrent average value in one stimulation period T into a voltage averagevalue. The determination circuit 1062 may determine whether the voltageaverage value mentioned above is between the preset positive voltageVTH+ and the preset negative voltage VTH−. If the above voltage averagevalue is between the preset positive voltage VTH+ and the presetnegative voltage VTH−, then the compensation circuit 1063 does not needto conduct charge compensation. If the voltage average value mentionedabove is not between the preset positive voltage VTH+ and the presetnegative voltage VTH−, then the compensation circuit 1063 conductscharge compensation to generate a compensation pulse current signal witha net charge amount, so that the total charge amount for neuralstimulation is within the safe charge amount range.

In the present embodiment, the detection circuit 1061 may be configuredto detect a total charge amount in one stimulation period T for thebidirectional pulse current signals generated by the current generator104. In some examples, the detection circuit 1061 may be formed by anintegral circuit. The integral circuit may integrate the charge of thebidirectional pulse current signals generated by the current generator104 within one stimulation period T, thereby obtaining the total chargeamount of the bidirectional pulse current signals in one stimulationperiod T.

As a specific example, if the absolute value of the total charge amountof the bidirectional pulse current signals generated by the pulsecurrent generation circuit 200 in one stimulation period T (e.g., theperiod is one second) exceeds 5×10−7 coulombs, then the compensationcircuit 1063 conducts charge compensation, i.e., when the currentaverage value of the bidirectional pulse current signals is greater than5×10−7 mA or less than −5×10−7 mA, then the compensation circuit 1063conducts charge compensation. If a resistance value of the secondresistor R2 is 10 kΩ, the preset positive voltage VTH+ may be 5 mv andthe preset negative voltage VTH− may be −5 mv. When the determinationcircuit 1062 determines that the voltage average value mentioned aboveexceeds 5 mv, the output end Out1 of the first voltage comparator U1outputs a high level and the output end Out2 of the second voltagecomparator U2 outputs a high level. When the determination circuit 1062determines that the voltage average value mentioned above is lower than−5 mv, the output end Out1 of the first voltage comparator U1 outputs alow level and the output end Out2 of the second voltage comparator U2outputs a low level. When the determination circuit 1062 determines thatthe voltage average value mentioned above is between −5 mv and 5 mv, theoutput end Out1 of the first voltage comparator U1 outputs a low leveland the output end Out2 of the second voltage comparator U2 outputs ahigh level.

In the present embodiment, the compensation pulse current signaloutputted by the output end of the compensation circuit 1063 is relatedto the first control end C+ of the compensation circuit 1063 and thesecond control end C− of the compensation circuit 1063. See Table 1below.

TABLE 1 Compensation pulse First control end C+ Second control end C−current signal High level High level Negative pulse Low level Low levelPositive pulse Low level High level None

When the determination circuit 1062 determines that the above voltageaverage value exceeds 5 mv, the compensation circuit 1063 needs tocompensate a negative pulse. At this moment, the output end Out1 of thefirst voltage comparator U1 outputs a high level and the output end Out2of the second voltage comparator U2 outputs a high level, i.e., thefirst control end C+ is a high level and the second control end C− is ahigh level, as shown in Table 1. The compensation pulse current signalgenerated by the compensation circuit 1063 is a negative pulse.

In addition, when the determination circuit 1062 determines that thevoltage average value mentioned above is lower than −5 mv, thecompensation circuit 1063 needs to compensate a positive pulse. At thismoment, the output end Outl of the first voltage comparator U1 outputs alow level and the output end Out2 of the second voltage comparator U2outputs a low level, i.e., the first control end C+ is a low level andthe second control end C− is a low level, as shown in Table 1. Thecompensation pulse current signal generated by the compensation circuit1063 is a positive pulse.

In addition, when the determination circuit 1062 determines that thevoltage average value mentioned above is between −5 mv and 5 mv, thecompensation circuit 1063 does not need to conduct charge compensation.The output end Out1 of the first voltage comparator U1 outputs a lowlevel and the output end Out2 of the second voltage comparator U2outputs a high level, i.e., the first control end C+ is a low level andthe second control end C− is a high level, as shown in Table 1. Thecompensation circuit 1063 does not conduct charge compensation.

In the present embodiment, FIG. 11 only shows a specific chargecompensation circuit according to a preferred embodiment of the presentinvention. The present embodiment is not limited to this. In the chargecompensation circuit 106, the implementation of the detection circuit1061, the determination circuit 1062 and the compensation circuit 1063may be varied in different forms.

In addition, the charge compensation method according to in the presentembodiment is a charge compensation method for conducting chargecompensation on the pulse current generation circuit 200. The pulsecurrent generation circuit 200 generates bidirectional pulse currentsfor neural stimulation. The charge compensation method includes:detecting the total charge amount during one stimulation period of thebidirectional pulse current signals generated by the pulse currentgeneration circuit 200; determining whether the total charge amountdetected by the detection circuit 1061 is less than or equal to the safecharge amount; and generating a compensation pulse current signal with anet charge amount when the determination circuit 1062 determines thatthe total charge amount exceeds the safe charge amount range, so thatthe total charge amount is within the safe charge amount range.

In addition, in the charge compensation method, when the determinationcircuit determines that the total charge amount is a positive value, acompensation pulse current signal with a negative compensation chargeamount is generated so that the total charge amount is within the safecharge amount range; and when the determination circuit determines thatthe total charge amount is a negative value, a compensation pulsecurrent signal with a positive compensation charge amount is generatedso that the total charge amount is within the safe charge amount range.Thus, the total charge amount for neural stimulation is more effectivelyensured to be within the safe charge amount range.

In some examples, when the determination circuit 1062 determines thatthe total charge amount of the bidirectional pulse current signalswithin one stimulation period T is positive, the compensation circuit1063 conducts negative charge compensation on the bidirectional pulsecurrent signals generated by the current generator 104. When thedetermination circuit 1062 determines that the total charge amount ofthe bidirectional pulse current signals within one stimulation period Tis negative, the compensation circuit 1063 may generate a positivecurrent pulse to conduct positive charge compensation on thebidirectional pulse current signals generated by the current generator104. In the above charge compensation process, the compensation circuit1063 preferably adopts a successive approximation charge compensationmethod, so as to gradually conduct charge compensation and enhance theaccuracy of charge compensation. For example, the compensation circuit1063 may generate a small current pulse to repeatedly conduct chargecompensation on the bidirectional pulse current signals generated by thecurrent generator 104. Herein, the net charge amount of the smallcurrent pulse generated by the compensation circuit 1063 may be positiveor negative.

In addition, in one preferred embodiment, a charge convergencecompensation method may be used to conduct charge compensation step bystep, so as to improve the accuracy of charge compensation. In someexamples, the detection circuit 1061 may detect the total charge amountof the bidirectional pulse current signals generated by the pulsecurrent generation circuit 200 within one stimulation period T. Thedetermination circuit 1062 may determine whether the absolute value ofthe total charge amount of the bidirectional pulse current signals inone stimulation period T is greater than the safe charge amount. Whenthe determination circuit 1062 determines that the absolute value of thetotal charge amount of the bidirectional pulse current signals in onestimulation period T is greater than the safe charge amount, thecompensation circuit 1063 conducts partial charge compensation. Forexample, when the determination circuit 1062 determines that the totalcharge amount of the bidirectional pulse current signals in onestimulation period T is Q1 and the absolute value of Q1 is greater thanQs (Qs is the safe charge amount), the compensation circuit 1063conducts partial charge compensation. Herein, the partial chargecompensation may be proportional charge compensation. For example,charge compensation is conducted according to proportion values such as30%, 40%, 50%, 60%, 70% and 80%.

For example, assuming that the safe charge amount is 5×10−8 coulombs,when the determination circuit 1062 determines that the total chargeamount of the bidirectional pulse current signals in one stimulationperiod T is negative charge of 1×10−7 coulombs, the compensation circuit1063 may conduct positive charge compensation according to a proportionof 50%, i.e., the compensation circuit 1063 may conduct positive chargecompensation of 5×10−8 coulombs. Then, the detection circuit 1061 maycontinue to detect the total accumulated charge amount generated by thepulse current generation circuit 200. If the determination circuit 1062determines that the total accumulated charge amount generated by thepulse current generation circuit 200 is negative charge of 6×10−8coulombs, the compensation circuit 1063 conducts positive chargecompensation of 3×10−8 coulombs. Next, the detection circuit 1061continues to detect the total accumulated charge amount generated by thepulse current generation circuit 200. When the determination circuit1062 determines that the total accumulated charge amount generated bythe pulse current generation circuit 200 exceeds the safe charge amountrange (5×10−8), the compensation circuit 1063 continues to conductcharge compensation according to a proportion of 50%; and thecompensation circuit 1063 stops charge compensation until thedetermination circuit 1062 determines that the absolute value of thetotal accumulated charge amount generated by the pulse currentgeneration circuit 200 is within the safe charge amount range. Ofcourse, after the compensation circuit 1063 stops charge compensation,the detection circuit 1061 may continue to detect the total accumulatedcharge amount generated by the pulse current generation circuit 200,i.e., the detection circuit 1061 may be always in a working state todetect in real time. Once it is detected that the charge amount exceedsthe standard (the absolute value of the total accumulated charge amountgenerated by the pulse current generation circuit 200 is greater thanthe safe charge amount), the compensation circuit 1063 may conductcharge compensation.

In some examples, the detection circuit 1061 may detect the total chargeamount of the bidirectional pulse current signals generated by the pulsecurrent generation circuit 200 within one stimulation period T. Thedetermination circuit 1062 may determine whether the total charge amountof the bidirectional pulse current signals in one stimulation period Tis greater than the safe charge amount. When the determination circuit1062 determines that the total charge amount of the bidirectional pulsecurrent signals in one stimulation period T is greater than the safecharge amount, the compensation circuit 1063 conducts partial chargecompensation. For example, when the determination circuit 1062determines that the total charge amount of the bidirectional pulsecurrent signals in one stimulation period T is Q1 and Q1 is greater thanthe safe charge amount, the compensation circuit 1063 conducts partialcharge compensation. Herein, the partial charge compensation may beproportional charge compensation. For example, charge compensation isconducted according to proportion values such as 30%, 40%, 50%, 60%, 70%and 80%.

For example, when the determination circuit 1062 determines that thetotal charge amount of the bidirectional pulse current signals in onestimulation period T is positive charge of 1×10−7 coulombs, thecompensation circuit 1063 may conduct positive charge compensationaccording to a proportion of 50%, i.e., the compensation circuit 1063may conduct negative charge compensation of 5×10−8 coulombs. Then, thedetection circuit 1061 may continue to detect the total accumulatedcharge amount generated by the pulse current generation circuit 200. Ifthe determination circuit 1062 determines that the total accumulatedcharge amount generated by the pulse current generation circuit 200 ispositive charge of 6×10−8 coulombs, the compensation circuit 1063 maycontinue to conduct negative charge compensation of 3×10−8 coulombs.Next, the detection circuit 1061 may continue to detect the totalaccumulated charge amount generated by the pulse current generationcircuit 200. When the determination circuit 1062 determines that thetotal accumulated charge amount generated by the pulse currentgeneration circuit 200 exceeds the safe charge amount range, thecompensation circuit 1063 may continue to conduct charge compensationaccording to a proportion of 50%; and the compensation circuit 1063 maystop conducting charge compensation on the pulse current generationcircuit 200 until the determination circuit 1062 determines that thetotal accumulated charge amount generated by the pulse currentgeneration circuit 200 is within the safe charge amount range. Ofcourse, after the compensation circuit 1063 stops charge compensation,the detection circuit 1061 may continue to detect the total accumulatedcharge amount generated by the pulse current generation circuit 200,i.e., the detection circuit 1061 may be always in a working state todetect in real time. Once it is detected that the charge amount exceedsthe safe charge amount range, the compensation circuit 1063 may conductcharge compensation.

While the present invention has been described in detail with referenceto the drawings and embodiments, it is understood that the descriptionmentioned above does not limit the present invention in any form. Thepresent invention may be modified and changed as needed by those skilledin the art without departing from the spirit and scope of the presentinvention, and such modifications and variations are within the scope ofthe present invention.

1. A pulse current generation circuit for neural stimulation,comprising: an analogue signal receiving device for receiving ananalogue signal; an analogue-to-digital converter for converting theanalogue signal into a digital control signal; a current signalcontroller for producing, according to the digital control signal, pulsecurrent parameters for generating bidirectional pulse current signals;and a current generator for generating, according to the pulse currentparameters, bidirectional pulse current signals for neural stimulation,wherein the current generator generates pulse currents of differentprecisions according to the pulse current parameters.
 2. The pulsecurrent generation circuit according to claim 1, wherein the totalcharge amount of the bidirectional pulse current signals is within asafe charge amount range during one stimulation period.
 3. The pulsecurrent generation circuit according to claim 1, wherein the pulsecurrent parameters comprise a negative pulse width, a negative pulseamplitude, a positive pulse width, a positive pulse amplitude and apulse interval.
 4. The pulse current generation circuit according toclaim 3, wherein the current generator generates a low-precision pulsecurrent or a high-precision pulse current according to the pulse currentparameters; and the current generator determines whether bidirectionalpulse current signals to be generated are less than a critical valueafter receiving the pulse current parameters, generates thehigh-precision pulse current when the bidirectional pulse currentsignals to be generated are less than or equal to the critical value,and generates the low-precision pulse current when the bidirectionalpulse current signals to be generated are greater than the criticalvalue.
 5. The pulse current generation circuit according to claim 4,wherein the current generator generates the high-precision pulse currentwhen the negative pulse width of the bidirectional pulse current signalsis greater than a preset duration and the negative pulse amplitude isless than or equal to the critical value.
 6. The pulse currentgeneration circuit according to claim 4, wherein the precision of thepulse amplitude of the high-precision pulse current is greater than theprecision of the pulse amplitude of the low-precision pulse current. 7.The pulse current generation circuit according to claim 1, wherein thetotal charge amount of the positive pulse current or the negative pulsecurrent during one stimulation period of the bidirectional pulse currentsignals is within the safe charge amount range.
 8. The pulse currentgeneration circuit according to claim 1, wherein the pulse currentgeneration circuit further comprises a charge compensation circuitconfigured to determine whether to conduct charge compensation on thecurrent generator according to the total charge amount during onestimulation period of the bidirectional pulse current signals, so as toensure that the total charge amount generated by the current generatoris within the safe charge amount range, the charge compensation circuitcomprising a detection circuit for detecting the total charge amountduring one stimulation period of the bidirectional pulse current signalsgenerated by the pulse current generation circuit; a determinationcircuit for determining whether the total charge amount detected by thedetection circuit exceeds the safe charge amount range; and acompensation circuit for generating a compensation pulse current signalwith a net charge amount when the determination circuit determines thatthe total charge amount exceeds the safe charge amount range, so thatthe total charge amount is within the safe charge amount range. 9-10.(cancelled)
 11. The pulse current generation circuit according to claim8, wherein in the compensation circuit, when the determination circuitdetermines that the total charge amount is a positive value, acompensation pulse current signal with a negative compensation chargeamount is generated so that the total charge amount is within the safecharge amount range; and when the determination circuit determines thatthe total charge amount is a negative value, a compensation pulsecurrent signal with a positive compensation charge amount is generatedso that the total charge amount is within the safe charge amount range.12. The pulse current generation circuit according to claim 8, whereinthe amplitude of the compensation pulse current signal is lower than apreset amplitude, and the period of the compensation pulse currentsignal is less than the period of the bidirectional pulse currentsignals.
 13. The pulse current generation circuit according to claim 12,wherein the preset amplitude is a minimum current amplitude which iscapable of playing a stimulation effect on the nerve tissue.
 14. Thepulse current generation circuit according to claim 8, wherein in thebidirectional pulse current signals, a waveform of a positive pulsecurrent signal is opposite to a waveform of a negative pulse currentsignal; and the detection circuit detects the charge amount of thepositive pulse current signal and an absolute value of the charge amountof the negative pulse current signal; and the determination circuitcompares the charge amount of the positive pulse current signal with theabsolute value of the charge amount of the negative pulse current signalto determine whether the total charge amount exceeds the safe chargeamount range.
 15. The pulse current generation circuit according toclaim 8, wherein the detection circuit detects an average value of thebidirectional pulse current signals generated by the pulse currentgeneration circuit; and the determination circuit determines whether anabsolute value of the average value is greater than a preset value; andwhen the absolute value of the average value is greater than the presetvalue, the compensation circuit generates a compensation pulse currentsignal with a net charge amount, so that the total charge amount iswithin the safe charge amount range.
 16. The pulse current generationcircuit according to claim 8, wherein the detection circuit detects acurrent average value of the bidirectional pulse current signalsgenerated by the pulse current generation circuit, and converts thecurrent average value into a voltage average value; and thedetermination circuit determines whether an absolute value of thevoltage average value is greater than a preset voltage value; and whenthe absolute value of the voltage average value is greater than thepreset voltage value, the compensation circuit generates a compensationpulse current signal with a net charge amount, so that the total chargeamount is within the safe charge amount range.
 17. The pulse currentgeneration circuit according to claim 13, wherein when the absolutevalue of the voltage average value is greater than the preset voltagevalue and the voltage average value is a positive value, thecompensation circuit generates a compensation pulse current signal witha negative net charge amount so that the total charge amount for neuralstimulation is within the safe charge amount range; and when theabsolute value of the voltage average value is greater than the presetvoltage value and the voltage average value is a negative value, thecompensation circuit generates a compensation pulse current signal witha positive net charge amount so that the total charge amount for neuralstimulation is within the safe charge amount range.
 18. The pulsecurrent generation circuit according to claim 8, wherein thecompensation circuit adopts a charge compensation method by successiveapproximation. 19-20. (canceled)
 21. An implantable electrical retinastimulator, comprising: an implanted device comprising the pulse currentgeneration circuit according to claim 1; a video recording deviceconfigured to capture a video image and convert the video image into avisual signal; a video processing device connected with the videorecording device and configured to process the visual signal to generatea modulation signal; and an analogue signal transmitting deviceconfigured to transmit the modulation signal to the implanted device,wherein the implanted device converts the received modulation signalinto the bidirectional pulse current signals used as electricalstimulation signals, so as to transmit the bidirectional pulse currentsignals for ganglion cells or bipolar cells of the retina to generate asense of light.
 22. (canceled)
 23. The implantable electrical retinastimulator according to claim 21, wherein the total charge amount of thebidirectional pulse current signals is within a safe charge amount rangeduring one stimulation period.
 24. The implantable electrical retinastimulator according to claim 21, wherein the pulse current parameterscomprise a negative pulse width, a negative pulse amplitude, a positivepulse width, a positive pulse amplitude and a pulse interval.
 25. Theimplantable electrical retina stimulator according to claim 21, whereinthe total charge amount of the positive pulse current or the negativepulse current during one stimulation period of the bidirectional pulsecurrent signals is within the safe charge amount range.